Shipboard Creepage and Clearance Analysis

OUSD (R&E) MODERNIZATION PRIORITY: General Warfighting Requirements (GWR) TECHNOLOGY AREA(S): Electronics OBJECTIVE: Develop test equipment to measure electrical properties related to shipboard environmental factors that affect creepage and clearance in Medium Voltage (MV) Naval electrical power systems. DESCRIPTION: Naval electrical power systems and associated high power combat systems are increasingly employing Medium Voltage (MV) power in the range of 1 to 35 kiloVolt (kV) AC or DC. Creepage and clearance requirements are a major driver in power density of MV equipment. Clearance is the shortest air distance between two exposed conductors while creepage is the distance along insulation surfaces between two exposed conductors. Setting these values too conservatively results in excessively large equipment; setting them too low results in equipment failure due to flashover. MVDC requirements have not yet been established, and the appropriateness of the MVAC requirements is not known. MVAC requirements are based on terrestrial commercial standards which have never been validated to apply to the marine environment. Naval ships have experienced arcing fault flashovers that have caused significant amounts of damage and lost operational time. The most significant factor for establishing safe clearance distances is the electrical properties of the air, which is affected by pollutants, salts, and other air contaminants. The air in different spaces onboard ship is certain to have varying electrical properties. Similarly, the most significant factor for establishing safe creepage distances is the electrical properties of the surface contaminants on insulators, which will vary significantly throughout the ship. Currently, there are no Navy or commercial products that are designed to measure creepage or clearance within a naval ship environment. The Navy seeks a portable testing apparatus to measure the electrical properties of air and surface contaminants onboard a naval ship at a threshold level of 20kV and objective of 35kV. A method is also needed to use these measurements as Objective Quality Evidence (OQE) for developing safe creepage and clearance requirements for inclusion in applicable equipment specifications and military standards. The portable testing apparatus measurements shall be accurate and repeatable enough to enable the Navy to employ the method to establish the creepage and clearance requirements. The Navy anticipates using multiple test apparatuses to create an initial survey of shipboard spaces over an extended period of time in operational conditions and industrial conditions. Following initial surveys, the Navy intends to employ the test apparatus in both prognostic and forensic procedures to understand the shipboard environment in specific ships. PHASE I: Provide a concept design for an apparatus that measures the electrical properties of air and surface contaminants onboard a naval vessel. Provide evidence, either through experimentation or simulation, that the concept design is feasible. Also provide a method to use measurements from the apparatus as Objective Quality Evidence (OQE) for developing safe creepage and clearance requirements for inclusion in applicable equipment specifications and military standards. The Phase I Option, if exercised, will include the initial design specifications and capabilities description to build a prototype apparatus in Phase II. PHASE II: Provide, demonstrate, and deliver an initial prototype apparatus that measures the electrical properties of air and surface contaminants onboard a naval vessel. Demonstrate the method to use measurements from the prototype apparatus as OQE for developing safe creepage and clearance requirements for inclusion in applicable equipment specifications and military standards. Based on feedback from demonstrations of the initial prototype apparatus, incorporate improvements in the apparatus design and produce two additional prototype apparatuses. Demonstrate these two prototypes function as intended and deliver to the U.S. Government. PHASE III DUAL USE APPLICATIONS: Support the Navy in transitioning the technology to Navy use. Update the prototype design to a final production configuration and develop supporting training documentation. The Government anticipates using multiple test apparatuses to create an initial survey of shipboard spaces over an extended period of time in operational conditions and industrial conditions. Following initial surveys, the Government intends to employ the test apparatus in both prognostic and forensic procedures to understand the shipboard environment in specific ships. This device should also prove useful in both the naval and commercial marine sectors to ensure the air and surface contaminants onboard ship are not more severe than for contaminants the shipboard equipment was designed for. REFERENCES: Damle, Tushar; Park, Chanyeop; Ding, Jeffrey; Cheetham, Peter; Bosworth, Matthew; Steurer, Mischa; Cuzner, Robert and Graber, Lukas. Experimental setup to evaluate creepage distance requirements for shipboard power systems. 2019 IEEE Electric Ship Technologies Symposium, Arlington VA, August 14-16, 2019. https://ieeexplore.ieee.org/abstract/document/8847827. Kaaiye, Sharif F. and Nyamupangedengu, Cuthbert. Comparative study of AC and DC inclined plane tests on silicone rubber (SiR) insulation. The Institution of Engineering and Technology, 20 April 2017. https://www.researchgate.net/publication/316518121_A_Comparative_Study_of_AC_and_DC_Inclined_Plane_Tests_on_Silicone_Rubber_SiR_Insulation. IEEE Recommended Practice for 1 kV to 35 kV Medium-Voltage DC Power Systems on Ships. IEEE Industry Applications Society and IEEE Power Electronics Society, IEEE Std 1709-2018, 27 September 2018. https://ieeexplore.ieee.org/document/8569023. KEYWORDS: Creepage; Clearance; Air Contamination Electrical Properties; Surface Contamination Electrical Properties; Medium Voltage; MV; MVAC; MVDC; Flashover